Your comments

You need to do two things first add the php.ini values and add an additional ngnix config value.

Website "Content Tab" (Add into php.ini values)
upload_max_filesize = 50M (Change 50M to your preferred upload size)

Website "Advanced Tab" (Add below to your custom configuration)
client_max_body_size 50M; (Change 50M to your preferred upload size)